Charged particle beam lithography apparatus for forming pattern on semi-conductor

ABSTRACT

In order to provide a high-speed and high accuracy cell projection exposure apparatus which increases a pattern projection number extremely, a plurality of stencil masks mounting a transferal aperture and a transmission aperture are provided and are positioned by a drive stage, the electron beam passes through a transmission aperture of other stencil masks while selecting the aperture on a stencil mask with a beam deflection device, the transmission aperture is provided for a mask transfer direction in succession, the stencil mask is moved while being transmitted with the beam, and other stencil mask transfer is executed when specified stencil mask aperture group is exposed. These operations are repeated so that all exposure processes are performed.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a charged particle beamlithography apparatus for forming a pattern on a semi-conductor memoryby utilizing a charged particle beam, and relates to a projection maskused for said charged particle beam lithography apparatus.

[0002] A conventional charged particle beam lithography apparatus,especially an electron beam lithography apparatus is used for researchand development as an exposure apparatus for exposing a minute patternreferring to its high resolution. In the mass-production of the deviceshowever, throughput of the charged particle beam lithography apparatusis low compared with that of an optical exposure apparatus, and the costperformance thereof is inferior.

[0003] Late years, a cell projection exposure method by which patternsare repeatedly loaded on a stencil mask beforehand, and the exposure isperformed in a high reduction rate by deflecting optically so as toselect the pattern, attracts attention. For example, such method isindicated in Japanese Patent Laid-open No. 6-163377. As in this cellprojection exposure method, the complicated shape patterns are exposedtogether, a shot number is reduced largely, and high throughput may beobtained.

[0004] Furthermore, this cell projection exposure method is possible toexpose in high accuracy too, because there is not a measurement settingerror (by location gap of mask) as in a variable shaped beam typeexposure beam formation method (Japanese Patent Laid-open No. 4-100208),in which the pattern that should be exposed is formed by overlapping twoor more masks.

[0005] However, the cell projection exposure method has a problem asthat only several ten patterns having exposure area of practically usedseveral um are obtained to be selected. In order to increase the patternnumber, a complicated pattern selecting deflection system which iscapable to be deflected with a great angle becomes to be needed,furthermore, there is a problem in accuracy such as distortion of astencil pattern and deterioration of matching accuracy and switchingaccuracy between mutual figures, because of aberration by an opticalseparating axis, deflection response, and increase of drift.

[0006] Moreover on a mask board top, in order to form a pattern whichexceeds a selection range of the optical system, a drive mechanism asindicated in Japanese Patent Laid-open No. 7-183191 may be arranged, ittakes an enough time for selecting the pattern by driving the mechanism,and there arises a problem in order to obtain the high throughput.

SUMMARY OF THE INVENTION

[0007] An object of the present invention is to solve the problemsstated above and is to provide a charged particle beam lithographyapparatus which remarkably increases the pattern number which can beselected by a cell projection exposure method and is capable to realizethe high throughput.

[0008] In order to solve the problems stated above, a charged particlebeam lithography apparatus in the present invention comprises a chargedparticle source to generate a charged particle beam, and a plurality ofstencil masks which respectively have several transferal aperturesgenerating patterns which should be projected on a specimen by a chargedparticle beam from the charged particle source. Thereby, in the casewhen projection is performed by a transferal aperture of at least one ofthe stencil mask among said several stencil masks, the charged particlebeam is irradiated on the specimen passing through outside of thetransferal aperture of other stencil masks among the several stencilmasks.

[0009] According to the constitution of the charged particle beamlithography apparatus stated above, it becomes possible to provide aplurality of stencil masks respectively having plural transferalapertures. Moreover there is no affection by the measurement settingerror of the stencil mask arranged in several steps too, and a lot oftransferal apertures becomes possible to be provided in high accuracy.

[0010] Moreover, as a constitution to realize a more concrete embodimentof the present invention, a transfer mechanism to transfer the stencilmask and a control part which controls a charged particle beam deflectorarranged in a circumference of an optical path of the transfer mechanismand the charged particle beam, are provided.

[0011] Furthermore, according to the present invention, a control partfor controlling the transfer mechanism is provided, and said controlpart moves an exposure location of the charged particle beam toward thetransferal aperture of the other stencil masks when the charged particlebeam is irradiated relating to the transferal apertures of one or morestencil mask.

[0012] Even if the stencil masks are provided in several steps, acontinuous writing using the plural transferal apertures may be realizedin high throughput.

[0013] Moreover, because this transfer is performed by the transfermechanism while the charged particle beam is positioned outside of atransmission aperture or the stencil mask, other stencil masks may beprojected before the next writing during the pictures are written by atleast one of the stencil mask.

[0014] As a transmission aperture is formed along the sequence of thetransferal aperture formed on the stencil mask furthermore, the exposurelocation of the charged particle beam moves to the neighborhood of thetransferal aperture which should be projected (or moves until saidtransferal aperture enters in a deflection range of the charged particlebeam) before the stencil mask moves, thereby, it becomes possible toposition the exposure location of the charged particle beam in thetransferal aperture immediately when the projection is performed byusing the transferal aperture.

[0015] Moreover, the plural stencil masks may be provided at an equalheight to an optical axis of charged particle beam. In this case, whenpatterns are written by the transferal aperture of one of the stencilmasks, the transfer mechanism is controlled so as to position thetransferal aperture of the other stencil masks in the deflection rangeof the deflector of the charged particle beam. Thereby, after thewriting by the transferal aperture of one of the stencil mask isfinished, the writing by next transferal aperture becomes possible to bedone immediately, and many transferal apertures may be provided whilemaintaining high throughput.

[0016] As stated above, the stencil masks arranged in several steps (orplural stencil masks in the same height) are provided, are positioned bythe transfer mechanism, and expose the transferal apertures on thestencil masks successively.

[0017] Moreover in order to realize the high throughput, whenselectively exposing the specified stencil mask aperture group by thecell projection deflector, the charged particle beam transmits thenon-screening parts of the other stencil mask (the transmissionaperture). Here, the stencil mask non-screening parts are provided insuccession towards a mask transfer direction, the other stencil mask areexecuted to be transferred when exposing the specified stencil maskaperture group while letting the beam transmit. The above statedoperations are repeated, thereby the exposure is controlled to complete.According to the above stated constitution of the present invention, itbecomes possible to reduce the transit time by the transfer mechanismwhich takes much time comparing with the exposure location transfer ofthe charged particle beam by the charged particle deflector, and toexpose continually by the cell projection exposure method.

[0018] The number of the apertures which are capable to be used in thepresent invention is limited by the product of the transferal aperturenumber of the stencil masks and the stencil mask number. For example,usual reduction rate is about one per several ten, and size of thestencil mask aperture to realize a cell projection exposure method ofseveral um is 100 um around. Accordingly when the transferal aperture isloaded by an occupation rate of 10%, it becomes possible to select 1000apertures with the stencil mask of 10 mm square. If plural stencil masksare arranged, it becomes possible to mount several thousand exposureapertures by the cell projection method.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is an illustrative view to explain the present invention.

[0020]FIG. 2 shows an embodiment of the present invention.

[0021]FIG. 3 is an illustrative view to explain the other embodiment ofthe present invention.

[0022] The FIG. 4 shows an example of the stencil mask shown in FIG. 3in the present invention.

[0023] The FIG. 5 shows an other embodiment in the present invention.

[0024] The FIG. 6 shows an example of the stencil mask shown in FIG. 5in the present invention.

[0025] The FIG. 7 shows an other embodiment further in the presentinvention.

[0026] The FIG. 8 shows an example of the stencil mask shown in FIG. 7in the present invention.

[0027]FIG. 9 show a flow chart which shows an operation example in thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028]FIG. 1 is a constitutional view of a variable shaped beam typeelectron beam lithography apparatus.

[0029] The electron beam that is irradiated from an electronic source 1generally passes through a limiting aperture 2 having a rectangularshape focuses on a stencil mask 5 by a shaping lens 4. A variablerectangle aperture and an aperture used for a cell projection exposuremethod are arranged on the stencil mask 5, and they are selected by anelectron beam deflection of a cell projection deflector 3. The electronbeam which has transmitted through an aperture on the stencil mask 5 soas to form a shaping beam 6, and is projected on a silicon wafer 10 soas to be reduced in a size of one per several ten by a reduction lens 7and an objective lens 9 Projection location onto the silicon wafer 10 isdesignated by a beam deflection with an objective deflector 8 and bypositioning a stage 11 with a drive system 12. Here, a transferalaperture number which is capable to be exposed is limited by anelectronic optical aberration and an output of a control circuit.

[0030]FIG. 2 is a figure to show a principle of the present inventionfor increasing the transferal aperture number which may be usedremarkably. The electron beam irradiated from the electronic source 1passes through a limiting aperture 2, and focuses on a first stencilmask 13 and a second stencil mask 14 which are movable independently andmechanically. In FIG. 2, although the stencil masks are arranged in twosteps, however they are capable to be arranged in three steps or more.Moreover the shaping lens etc. are omitted in FIG. 2. In the same way asin FIG. 1, a transferal aperture 15 for the cell projection exposuremethod including an aperture for a variable rectangle is arranged on thestencil mask. The transferal aperture 15 and the transmission aperture16 are formed along a transfer direction of the stencil mask, and isarranged in a beam deflection range of the cell projection deflector 3.In the writing, a desired aperture is selected from a plural transferalapertures group in the deflection range by cell projection deflector 3.When either transferal aperture 15 of the first stencil mask 13 and thesecond stencil mask 14 is selected, it is set up so that an exposurelocation of the electron beam is positioned to the transmission aperture16 of the other stencil mask.

[0031] In order to reduce a transfer dead time here, while thetransferal aperture 15 of an either stencil mask is selectively exposed,the beam transmits to the transmission aperture 16 of the other stencilmask and at the same time moves to the next exposure location. Byrepeating the above-mentioned operation, it becomes possible toselectively expose a lot of transferal apertures 15.

[0032] In the same way as FIG. 1, a high-speed writing is realized bypositioning the shaping beam 6 transmitted through the transferalaperture 15 provided on the second stencil mask 14, on the silicon wafer10 by the objective deflector 8 and the stage 11. The transferalaperture 15 is arranged according to a writing order of the exposurepattern 18, and the transmission aperture 16 is formed in succession toa transfer direction. That is, in an electron beam lithography apparatusby a continuation transfer system, the exposure pattern 18 is divided soas to be exposed successively on an exposure stripe 17 in a deflectionwidth of objective deflector 8. The stencil mask aperture may beeffectively moved by arranging the transferal aperture 15 in the writingorder.

[0033] In this way, as the transferal aperture 15 is arranged in a lineor few lines, furthermore, the transmission aperture 16 is arrangedalong the sequence (line or lines), if the stencil masks of severalsteps are provided, a high throughput becomes possible to be realized.This is because the exposure location of the electron beam is capable tomove to neighborhood of the transferal aperture which should be used inthe next among the transferal aperture except the stencil mask used forthe projection.

[0034] Furthermore, as for the transmission aperture 16 is continuallyformed along the sequence which the transferal aperture 15 forms, theelectron beam is not intercepted while being projected. By transferringin this way, a change of the transferal aperture becomes possible to beoperated immediately.

[0035] As shown in FIG. 2 in this description in addition to above, thestencil mask in which the transferal aperture is formed laterally inlonger is explained as an example, however, there is no need to alwayslet the exposure location move by using the transmission aperture 16 inthe case using such a stencil mask as above, and the beam may betransferred to the next exposure location while letting the beamtransmitted outside space of the stencil mask, for example. Because, thestencil mask is formed along the arrangement of the transferal aperturein the outside space of the stencil mask in the same way as thetransferal aperture, an effect similar to that obtained when thetransmission aperture is used, may be obtained.

[0036] In the example shown in FIG. 2 in addition to above, transfermechanisms 30, 31 are respectively provided on the first stencil mask 13and the second stencil mask 14, and support them so as to make themmovable to a horizontal direction shown by arrows of FIG. 2. As for thetransfer mechanisms 30, 31, transfer control parts 26, 27 arerespectively provided, and they supplies signals to the transfermechanism 30, 31 so as to drive them according to a transfer quantitythereof based on a stencil mask transfer command from a control computer28.

[0037] Moreover, in FIG. 2, the transfer mechanism is shown so as tomove to only the direction shown by an arrow, however, the direction isnot limited to this direction. For example, as the transfer mechanism totransfer the electron beam between the transferal aperture 15 and thetransmission aperture 16, a transfer mechanism to move the stencil maskto a vertical direction being vertical to the arrow may be provided.Moreover, this transfer mechanism may be used to transfer between thetransferal apertures of the stencil mask formed two lines or moretransferal apertures.

[0038] Furthermore, in the following explanatory drawings, the size andthe arrangement of the aperture is shown by being fixed, however it isself-evident that it may be variable according to the exposure pattern18. For example, when the repeating pattern that should be exposed isbigger than the limiting aperture 2, the transferal aperture 15 isscanned over with the cell projection deflector 3, and the otherpertinence transmission aperture 16 may be magnified than the exposurerange. Moreover, when the repeating pattern is partially more minutethan the limiting aperture, if the transferal aperture 15 of the firststencil mask 13 arranged on an upper line is used as the limitingaperture the transferal aperture size of the second stencil mask 14arranged on an lower line may be reduced so as to increase the number ofthe aperture.

[0039] FIGS. 3 to 8 show the embodiments of the present invention. FIG.3 is an example in which the first stencil mask 13 and the secondstencil mask 14 shown in FIG. 2 is arranged to establish a gap withinthe depth of focus. Generally, an incidence angle of the electron beamlithography apparatus is small on the specimen side so as to be in adepth of focus of several 10 um. As having a reduction optical systemfurthermore, the location margin of the stencil mask in the optical axisdirection thereof is about several 100 um, and it is easy to disposethem closely. When it is not easy to dispose them closely because of anyother condition, it is possible to move mutually by inserting anelectron lens between the first stencil mask 13 and the second stencilmask 14. A stencil mask example to be used in this embodiment is shownby FIG. 4.

[0040]FIG. 4 show an example in which the transferal aperture 15 and thetransmission aperture 16 are arranged closely in few lines. Eachaperture size may be adjusted finely according to the transferalaperture size. This stencil mask may be produced by a usual silicon maskprocess. That is, after having formed the aperture by a dry etchingmethod on the silicon surface, a thin film is formed by a back etchingmethod from a reverse face of the silicon. According to this productionmethod, the lib structure for obtaining needed strength security andthermal diffusion may be formed easily, it becomes possible to formseveral aperture groups which may be selected continuously as shown inFIG. 4

[0041]FIG. 5 is an example in the present invention in which a firstcell projection deflector 19 and a second cell projection deflector 20are respectively provided between the limiting aperture, the firststencil mask 13 and the second stencil mask 14 in FIG. 2. Moreover, thedeflection control parts 32,33 are respectively provided to thesedeflectors, the signal is supplied in the first cell projectiondeflector 19 and the second cell projection deflector 20 so as to applya voltage according to a deflection quantity based on a deflectioncommand of the electron beam from the control computer 28. The selectivedegree of freedom is improved furthermore by providing the second cellprojection deflector 20. The patterns which is capable to be selected bythe deflection are increased in double as shown the deflection range ofthe projection deflection in dotted lines of FIG. 5 compared with thatin FIG. 3.

[0042] An example of the stencil mask used in this embodiment is shownin FIG. 6. FIG. 6 shows an example same as FIG. 4 in which thetransferal aperture 15 and transmission aperture 16 are arranged closelyin several lines. Aperture selection by the deflection and mechanicalaperture transfer are repeated in the writing sequence with the mutualstencil mask.

[0043]FIG. 7 shows an example in which the first parallels stencil mask13 driven by the first projection drive system 21 and the secondprojection drive system 22 independently driven by the second stencilmask 14 are moved in parallel. The control system is omitted in thisfigure.

[0044] Stencil mask configuration example to use with this embodiment isshown by FIG. 8. FIG. 8 shows an example in which a variable rectangularaperture 24 used frequently and a transferal aperture 15 appearingfrequently as a fixed location, and a transferal aperture 15 arearranged closely in several lines. Because the transmission aperture isunnecessary in this embodiment, the stencil mask may be miniaturized.The aperture selection performed by deflection in the writing sequence,and the mechanical aperture transfer is repeated by a mutual stencilmask. The mechanical transfer is capable to be performed by one axesposition control by using the laser measuring system 23 etc., and whenthe rotation error in the projection drive is big, a position controlsystem more than 2 axes is applied. In any event, an error of thepositioning may be revised by the beam deflection system easily becauseof its high reduction rate. Moreover, the selective deflection range maybe reduced and it is arranged with the writing sequence reasonablyfurthermore, a large beam deflection being disadvantageous in accuracymay be prevented and stabilization of the exposure location accuracy ispossible to be obtained, too. Moreover, the time zone while theprojection by one stencil mask is performed, may be used in the transittime of the other stencil mask, thereby the transit time may be reduced.

[0045]FIG. 9 is a flow chart of the writing process by the constitutionshown by FIG. 5 and FIG. 6.

[0046] Starting the writing, the mask stage moves so that the shapingbeam 6 is positioned in the transferal aperture of the first stencilmask and the transmission aperture of the second stencil mask (step 90in FIG. 9). In FIG. 5, the transfer mechanism is omitted.

[0047] The displacement from the objective location of the mask stagelocation is measured by a stage location measuring means such as a lasercoordinate measuring apparatus etc. (it is not illustrated in thefigure), and it is fed back to the cell projection deflector or theobjective deflector in the writing. That is, on the basis of themeasured mask stage location error, the exposure location of injectionlocation and specimen surface to the aperture illumination location ofthe first stencil mask and the second stencil mask transmission apertureare revised at high speed by respectively the first cell projectiondeflector 19, the second cell projection deflector 20 and the objectivedeflector (step 91 in FIG. 9).

[0048] Corresponding to the exposure pattern signal from the controlpart 28, and based on the transferal aperture position informationmemorized beforehand, the first cell projection deflector 19 selects atransferal aperture on the first stencil mask 13, and the exposure ofthe wafer is performed repeatedly. Here, the transferal aperture isselected and exposed in a dotted line department of the first stencilmask 13 as a selective range of the first cell projection deflector 19(when the stencil mask is not projected).

[0049] While exposing the first stencil mask aperture, the secondstencil mask 14 is moved toward the next exposure planned transferalaperture without passing trough the transmitting aperture edge. That is,while the beam is positioned in the transmission aperture 16 (so thatthe second stencil mask 14 does not disturb orbit of the beam), thesecond stencil mask 14 moves by the transfer mechanism(steps 92 to 93 inFIG. 9). Then, the transferal aperture having a pattern which should beexposed in the next, stops to move at a point in time that is positionedin a selective range of the second cell projection deflector 20 (dottedline department) (steps 94 to 96 in FIG. 9).

[0050] Every stencil mask stopping errors are solved easily bycorrecting the mask stage location measurement system to the everydeflection systems. Because if the selective range by the deflectiondevice is fitted to the location of the transferal aperture which shouldbe projected in the next at least, even if the transfer by the transfermechanism is not completed or it is projected over, it may be revised insuitable by transferring the exposure location of the charged particlebeam by the deflection device.

[0051] As a concrete constitution for it, it may be proposed a means fordetermining a control output supplied to the deflection device based ondeficiency or excess of the transfer provided as the positioninformation of the stage from said stage location measurement means.Moreover the timing that provides such an operation may be not only thecase for the correction of the location error mentioned above, but thecase as follows,

[0052] For example, when the projection by the first stencil mask 13 iscompleted before the location transfer of the second stencil mask 14 iscompleted, the time during the transfer of the second stencil mask 14after that, becomes to be the time zone not to be projected. In order toeliminate this time zones a little, even if it is before the transfer ofthe stencil mask is completed, the projection may be started when thetransferal aperture having the pattern which should be projected in thenext is positioned in the deflection range of the charged particle beam.

[0053] Here, the transfer into a deflection region of each mask stage isdetected by a function for measuring the mask stage coordinate, and themechanical location thereof is revised with the deflection system,thereby the exposure is capable to be started without always completingthe movement of the mask stage to the deflection center. The mechanicaltransit time may be shortened as stated above. Moreover, as thedeflector is capable to be operated extremely at high speed, the maskstage is controlled to be moved continuously with a speed in inverselyproportional to the exposure number (exposure time) by the aperture, themeasurement location data is corrected with a real time, and it ispossible to continuously transfer the mask stage so as to make thewaiting time for the stage transfer minimum.

[0054] Based on the condition as stated above, the exposure is repeated,or the projection exposure of the transferal aperture 15 of the secondstencil mask 14 is repeated after finishing the transfer to the rangecapable to be exposed of the second stencil mask 14, and the chip or thestripe finish to be exposed (step 97 to 99 in FIG. 9).

[0055] In order to expose with a high throughput as stated above, it ispreferable to arrange the transferal aperture on the stencil mask in anexposing order. Concretely, preparing the transferal aperture having aprojection pattern to be exposed in a selected range of the cellprojection deflector in succession, the stencil mask is changed at atime point when the projection by those transferal apertures hasfinished once. Moreover, relating to the order to write the wafer, thewafer stage is moved to be exposed in a direction to make a substitutionnumber of the aperture projection fewer, thereby the number of theapertures may be reduced, too.

[0056] The transit time of the transfer mechanism may be proposed to bereduced as one condition to get high throughput. Stepping motors areused for the transfer mechanism generally, however it takes about 100 mstransit time which is almost 100000 times is needed comparing with anexposure location transit time of 1 us of the electron beam by thedeflecting electrode, and the throughput differs greatly depending onhow the time is eliminated.

[0057] In order to improve the throughput in this embodiment, the otherstencil mask is moved by the transfer mechanism while the projection isperformed by the other stencil mask, thereby the transit time by thetransfer mechanism is reduced and high throughput is realized. Moreover,it is one means to reduce the transit time by the transfer mechanism tosupplement a transfer location error of the transfer mechanism statedabove by the deflector.

[0058] Ideally, if the transfer of the other stencil mask is completedduring the projection with a stencil mask of the other, it becomespossible to substantially save the moving time of the transfermechanism.

[0059] Moreover, the arrangement of the transferal aperture of thestencil mask will be assigned to each stencil mask according to thetransferal aperture group (deflection range of the deflector forexample) so that the other stencil mask is capable to move while thestencil mask of the other is exposed.

[0060] According to the present invention as stated above, as sizesetting error does not occur even if several stencil masks are provided,A lot of transferal apertures may be provided in a high accuracy, andthe number of the patterns to be exposed together becomes possible to begreatly increased.

[0061] Moreover as the time for selecting the transferal aperture of theplural stencil masks may be reduced, it becomes possible to improve thethroughput.

[0062] Moreover, it becomes possible to be used in a logic circuit whichis partially exposed together with a few patterns to be repeated.Moreover, the exposure location accuracy is possible to be performed instable too because the selective deflection range is reduced.

What is claimed:
 1. A charged particle beam lithography apparatuscomprising: a charged particle source to generate a charged particlebeam; an objective deflector for deflecting said charged particle beam;and a plurality of stencil masks, each of said stencil masks havingseveral transferal apertures and a transmission aperture, wherein saidtransferal apertures are formed at least two lines.